The Interrelationship of Heterodera schachtii and Ditylenchus dipsaci on Sugarbeet

Heterodera schachtii significantly (P = 0.05) reduced sugarbeet root growth below that of uninoculated controls at 20, 24, and 28 C, and Ditylenchus dipsaci significantly (P = 0.05) reduced root growth below that of uninoculated controls at 16, 20, 24, and 28 C. A combination of H. schachtii and D. dipsaci significantly (P = 0.05) reduced root growth below that of single inoculations of H. schachtii at all temperatures and D. dipsaci at 20, 24, and 28 C. Single inoculations of H. schachtii and D. dipsaci significantly (P = 0.05) reduced top growth of sugarbeet below that of uninoculated controls at 20, 24, and 28 C, and 16, 20, 24, and 28 C, respectively. A combination of the two nematodes significantly (P = 0.05) reduced top growth below that of single inoculations of H. schachtii at all temperatures. However, a combination of the two nematodes failed to significantly (P = 0.05) reduce top growth below that of single inoculations of D. dipsaci at any temperature. Inoculations of either H. schachtii or D. dipsaci did not affect penetration of the other nematode, and D. dipsaci did not affect development and reproduction of H. schachtii. D. dipsaci did not reproduce on sugarbeet.     

Relationship Between Heterodera schachtii,Meloidogyne hapla,and Nacobbus aberrans on Sugarbeet

Heterodera schachtii, Meloidogyne hapla, and Nacobbus aberrans either alone, or in various combinations with each other, can, when inoculated at a concentration of 12 second-stage juveniles/ cm³ of soil, cause a significant (P = 0.01) suppression of growth of sugarbeet (cv. Tasco AH14) seedlings. M. hapla and H. schachtii decreased growth of sugarbeet more than N. aberrans over a 60-day period. The adverse effect of N. aberrans on the final population/initial population (Pf/Pi) ratio for either M. hapla or H. schachtii was dependent on time, and was more accentuated on that of M. hapla than on that of H. schachtii. Neither M. hapla nor H. schachtii had an adverse effect on the Pf/ Pi ratio of N. aberrans. N. aberrans is considered to be less aggressive on sugarbeet than either H. schachtii or M. hapla. Sections of sugarbeet roots infected simultaneously with H. schachtii and N. aberrans showed scattered vascular elements between the N. aberrans syncytium located in the central part of the root and that of H. schachtii in the peripheral position.     

Effects of Oxime Carbamate Nematicides on Development of Heterodera schachtii on Sugarbeet

Treatment of sugarbeet, Beta vulgaris L., with aldicarb, aldicarb sulfoxide, or aldicarb sulfone 10 days after plants were inoculated with Heterodera schachtii prevented development of the nematode, but second-stage larvae penetrated the roots. These chemicals had no measurable effects on nematodes in plants treated 15 days after inoculation. The tests established that soil treatments of aldicarb are directly or indirectly lethal to larvae developing within roots of sugarbeet. Heterodera schachtii failed to develop on root slices of red table beet grown in soil treated with aldicarb or aldicarb sulfoxide. Similar treatment of plants with aldicarb sulfone or oxamyl did not affect subsequent development of H. schachtii on root slices of treated plants.     

The Relationship of Plant Age,Soil Temperature,and Population Density of Heterodera schachtii on the Growth of Sugarbeet

There were direct relationships between inoculum density of Heterodera schachtii Schm. (nematode population density), initial soil temperature, the growth of sugarbeets in the greenhouse under controlled temperatures, and nematode populations. Heterodera schachtii was least pathogenic on plants inoculated at 6 wk of age and most pathogenic on plants grown from inoculated germinated seed (0 wk of age). In the field, H. schachtii was least pathogenic on sugarbeets grown at an initial soil temperature of 6 C and most pathogenic on those grown at an initial soil temperature of 24 C. The growth period for sugarbeets at the different soil temperatures was determined by heat units; since penetration of sugarbeet roots by H. schachtii larvae is accelerated at soil temperatures above 10 C, each hour-degree ahove 10 C was counted as one effective heat unit (HU). Using this guideline it was determined that root weight depressions in the greenhouse, for each degree-unit population (HU-UP) where unit population = one larvae/g soil, were 0.052, 0.09, 0.12, and 0.17 mg at initial soil temperatures of 6, 12, 18, and 24 C, respectively. Root weight depressions were 0.28, 0.23, 0.15, and 0.086 mg when plants were inoculated at 0, 2, 4, and 6 wk of age.     

A Simulation Model of Heterodera schachtii Infecting Beta vulgaris

A simulation model of a single sugarbeet, Beta vulgaris L., plant infected by the sugarbeet cyst nematode, Heterodera schachtii Schmidt, was developed using published information. The model is an interactive computer simulation programmed in FORTRAN. Given initial population densities of the nematode at planting, the model simulates nematode population dynamics and the growth of plant tap and fibrous roots. The driving variable for nematode development and plant growth is temperature.     

Comparative Morphometrics of Eggs and Second-Stage Juveniles of Heterodera schachtii and a Race of H. trifolii Parasitic on Sugarbeet in The Netherlands

Measurements of second-stage juveniles of Heterodera schachtii from California and The Netherlands and a race of H. trifolii from The Netherlands were obtained and compared to determine if these populations can be differentiated by morphometrics. Juvenile lengths of 10 specimens from each of 10 cysts of each population were measured. Dimensions of tail regions of 20 juveniles from individual cysts of H. schachtii (California) and a like number of juveniles of H. trifolii (The Netherlands) were also obtained. The mean lengths of juveniles of H. schachtii from California and The Netherlands were not significantly different, but similar measurements of H. schachtii and H. trifolii were different (P = 0.05). Mean dimensions of tail lengths, tail widths, tail hyaline lengths, and tail length/tail width were significantly greater for H. trifolii than for H. schachtii. Also, dimensions of eggs of H. trifolii were significantly greater than dimensions of H. schachtii eggs. The investigations established that H. schachtii can be readily differentiated from H. trifolii by morphometrics of eggs and juveniles, Minimum sample sizes required for specified confidence intervals for each criterion measured are provided.     

The Effects of Hot Water Treatments on Survival of Heterodera schachtii

Cysts of Heterodera schachtii were treated in a water bath at constant temperatures ranging from 45 - 62.5 C for 1 sec to 28 hr. Treated and untreated cysts were incubated 8 weeks in sugarbeet root diffusate at 24 C to measure emergence of surviving larvae. Within the temperature range of 49 - 54 C, the minimum lethal temperature was proportional to the log time of treatment. No larvae emerged from cysts exposed 10 sec at 60 C. Although treatment of cysts for 8 hr at 45 C significantly reduced emergence, increasing the treatment period to 28 hr did not completely suppress emergence.     

The Relationship Between Population Density of Heterodera schachtii,Soil Temperature,and Sugarbeet Yields

In two glasshouse experiments, relations between sugarbeet root dry weight (y, expressed as a percentage of the maximum dry root weight), and preplanting populations of Heterodera schachtii (P_i) were described by the equation y = 100(Z)^P_i-T, in which Z = a constant slightly smaller than 1, and T = the tolerance limit (the value of P_i below which damage was not measureable). T varied with temperature; it was 65 eggs/100 g soil at 23 and 27 C and 430 eggs/100 g soil at 19 C. At 15 and 31 C there was no loss of root dry weight up to the maximum preplanting populations tested. In a field experiment in the Imperial Valley the relation between root yield (y) and P_i was y = 100 (0.99886)^P_i - 100, and the tolerance limit was 100 eggs/100 g soil.     

Interrelationship of Heterodera schachtii and Meloidogyne hapla on Tomato

Invasion of tomato (Lycopersicon esculentum L.) roots by combined and sequential inoculations of Meloidogyne hapla and a tomato population of Heterodera schachtii was affected more by soil temperature than by nematode competition. Maximum invasion of tomato roots, by M. hapla and H. schachtii occurred at 30 and 26 C, respectively. Female development and nematode reproduction (eggs per plant) of M. hapla was adversely affected by H. schachtii in combined inoculations of the two nematode species. Inhibition of M. hapla development and reproduction on tomato roots from combined nematode inoculations was more pronounced as soil temperature was increased over a range of 18-30 C and with prior inoculation of tomato with H. schachtii. M. hapla minimally affected H. schachtii female development, but there was significant reduction in the buildup of H. schachtii when M. hapla inoculation preceded that of H. schachtii by 20 days.     

Effect of Phenamiphos on Heterodera schachtii and Meloidogyne javanica

Aqueous solutions of technical-grade phenamiphos [ethyl 3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoratnidale] were used in hatching chambers to test, under laboratory tory conditions, the effect of phenamiphos on the hatching and movement of Meloiclogyne javanica and Heterodera schachtii. Hatch of M. javanica and H. schachtii eggs was depressed 70 and 88% by nematicide at 0.48 and 4.80 μg/ml, respectively. The infectivity of second-stage larvae of both species was affected by concentrations as low as 0.01 μg/ml. At least 0.5 μg/ml was required to decrease the movement of larvae of M. javanica and H. schachtii. To decrease the movement of H. schachtii males toward females, 10 μg/ml was required. In a field experiment using a 15% granular formulation, 5 kg/ha a.i. significantly reduced infection of sugarbeet roots by H. schachtii.     

Improved Methods of Hatching Heterodera schachtii Larvae for Screening Chemicals

The rate of hatching of Heterodera schachtii larvae was greatly increased by placing cysts in sieves enclosed by small disposable cups. An apparatus that permitted rapid storage of second-stage larvae at 10 C prolonged the viability of the larvae.     

In-Vitro and In-Vivo Effects of Aldicarb on Survival and Development of Heterodera schachtii

Aqueous solutions of 5-500 μg/ml aldicarb inhibited hatching of Heterodera schachtii. Addition of hatching agents, zinc chloride, or sugarbeet root diffusate, to the aldicarb solutions did not decrease the inhibition of hatching. When cysts were removed from the aldicarb solufions and then treated for 4 wk in sugarbeet root diffusate, larvae hatched and emerged. Treatments of newly hatched larvae of H. schachtii with 5-100 μg/ml aldicarb depressed later development of larvae on sugarbeet (Beta vulgaris). Similar treatments with aldicarb sulfoxide had less effect on larval development, and aldicarb sulfone had no effect. Numbers of treated larvae that survived and developed were inversely proportional to concentration (0.1-5.0 μg/ml) and duration (0-14 days) of aldicarb treatments. Development of H. schachtii on sugarbeet grown in aldicarb-treated soil was inversely proportional to the concentration of aldicarb in the tested range of 0.75 - 3.0 μg aldicarb/g of soil. Transfer of nematode-infected plants to soil with aldicarb retarded nematode development, whereas transfer of plants first grownin treated soil to nematode-infested soil only slightly suppressed nematode development. Development of H. schachtii was inhibited in slices of storage roots of table beet (B. vulgaris), sugarbeet and turnip, (Brassica rapa), that had grown in soil treated with aldicarb.     

Suppression of Heterodera schachtii Populations by Dactylella oviparasitica in Four Soils

The effects of Dactylella oviparasitica strain 50 applications on sugarbeet cyst nematode (Heterodera schachtii) population densities and plant weights were assessed in four agricultural soils. The fungus was added to methyl iodide-fumigated and nonfumigated portions of each soil. The soils were seeded with Swiss chard. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). Approximately 1,487 degree-days after infestation, H. schachtii cyst, egg and J2 numbers and plant weights were assessed. In all four fumigated soils, D. oviparasitica reduced all H. schachtii population densities and increased most of the plant weights compared to the nonamended control soils. In two of the nonfumigated soils (10 and SC), D. oviparasitica reduced H. schachtii population densities and increased most plant weight values compared to the nonamended control soils. For the other two nonfumigated soils (44 and 48), which exhibited pre-existing levels of H. schachtii suppressiveness, fungal applications had relatively little impact on H. schachtii population densities and plant weights. The results from this study combined with those from previous investigations suggest that D. oviparasitica strain 50 could be an effective biological control agent.     

Arabidopsis peroxidase AtPRX53 influences cell elongation and susceptibility to Heterodera schachtii

Cyst nematodes establish and maintain feeding sites (syncytia) in the roots of host plants by altering expression of host genes. Among these genes are members of the large gene family of class III peroxidases, which have reported functions in a variety of biological processes. In this study, we used Arabidopsis-Heterodera schachtii as a model system to functionally characterize peroxidase 53 (AtPRX53). Promoter assays showed that under non-infected conditions AtPRX53 is expressed mainly in the root, the hypocotyl and the base of the pistil. Under infected conditions, the AtPRX53 promoter showed upregulation at the nematode penetration sites and in their migration paths. Interestingly, strong GUS activity was observed in H. schachtii-induced syncytia during the early stage of infection and remained strong in the syncytia of third-stage juveniles. Also, AtPRX53 showed upregulation in response to wounding and jasmonic acid treatments. Manipulation of AtPRX53 expression through overexpression and knockout mutation affected both plant morphology and nematode susceptibility. While AtPRX53 overexpression lines exhibited short hypocotyls, aberrant flower development and reduced nematode susceptibility to H. schachtii, the atprx53 mutant showed long hypocotyls and a 3-carpel silique phenotype as well as a non significant increase of nematode susceptibility. Taken together these data, therefore, indicate diverse roles of AtPRX53 in the wound response, flower development and syncytium formation.     

Factors Affecting the Biology and Pathogenicity of Heterodera schachtii on Sugarbeet

A direct relationship exists between soil temperature and Heterodera schachtii development. The average developmental period of two nematode populations from Lewiston, Utah, and Rupert, Idaho, from J2 to J3, J4, adult, and the next generation J2 at soil temperatures of 18-28 C were 100, 140,225, and 399 degree-days (base 8 C), respectively. There was a positive relationship (P < 0.05) between nematode Pi, nematode generations, and sugarbeet yields. The greatest sugarbeet growth inhibition (87%) occurred when sugarbeets were exposed to a Pi of 12 eggs/cm³ soil for five generations (1,995 degree-days), compared with a 47% inhibition when plants were exposed to the same Pi for two generations. There was a negative correlation (P < 0.05) between the Pi, Pf, and sugarbeet yield for each population threshold. The smaller the Pi, the greater the sugarbeet yields and the greater the Pf. Root yields were 80 and 29 t /ha and Pf were 8.4 and 3.6 eggs/cm³ soil when sugarbeet seeds were planted at Pi of 0.4 and 7.9 eggs/cm³. respectively, at a soil temperature of 8 C. The number of years rotation with a nonhost crop required to reduce the nematode population density below a damage threshold level of 2 eggs/cm³ depends on the Pi. A Pi of 33.8 eggs/cm³ soil required a 5-year crop rotation, whereas a Pi of 8.4 eggs/cm³ soil required a 2-year crop rotation.     

The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984–86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation
Y = Ymin + (Ymax - Ymin) Z^pi-T
Fixing T = 200 eggs + juveniles 100 g^-1 soil and Z^T= 0.95, estimated values of Ymax varied from 49.2–67.1 t ha^-1 (129– 155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5–53.9 t ha^-1 (27–94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha^-1.     

Persistence of Activity of Oxamyl Against Heterodera schachtii on Cabbage

The duration of effectiveness of a foliar spray of oxamyl against Heterodera schachtii and the location of the protective effect were determined by applying a foliar spray at 0.04 kg (a.i.)/100 liters of water to cabbage seedlings. Oxamyl, or a metabolite of oxamyl, apparently is translocated to anti becomes prolective in the root within 7 days. Between 7 and 14 days, the location of the protection shifts from within the root In the root surface or rhizosphere. The chemical remains active for at least 21 days unless it is removed from the root or rhizosphere by washing with water.     

Population Dynamics of Heterodera schachtii on Tomato and Sugar Beet

Experiments showed that development of male and female Heterodera schachtii on tomato and sugarbeet are disproportionately influenced by the nematode inoculum level and root size, which together determine the density of invading larvae. Slight overcrowding favored development of males over females, whereas severe overcrowding equally affected development of males and females. Differential population changes of host-selected races on tested cultivars was attributable to selective development of male and female nematodes.     

Tolerance of Soybean to Heterodera glycines

Seven soybeans were selected from 200 entries evaluated for tolerance to soybean cyst nematode (SCN), Heterodera glycines. Tolerance to SCN was measured by comparing the seed yield from aldicarb-treated vs. nontreated plots. A yield response index (YRI) was calculated for each entry: YRI = (seed yield from nontreated plot/seed yield from treated plot) × 100. The soybean entries Coker 156, PI 97100, and S79-8059 exhibited high tolerance (YRI) to SCN when compared to Essex even though they became heavily infected with SCN. Tolerance in soybeans to SCN may be useful in pest management programs designed to stabilize soybean yield.